The present invention relates to rare earth oxysulfide particulate materials, and particularly relates to terbium-activated rare earth oxysulfide phosphors exhibiting an enhanced green:blue emission ratio as well as a method for producing such enhancement.
Rare earth oxysulfides have long been recognized in the art as valuable luminescent materials. These phosphors are in the form of a solid solution having a matrix of the rare earth oxysulfide compound with a small amount of an activator or dopant dispersed throughout the matrix. The activator normally is also a rare earth element.
Among such rare earth activated rare earth oxysulfides are the blue-green emitting terbium-activated rare earth oxysulfides having the nominal formula: EQU M.sub.2-x O.sub.2 S: xTb (1)
where x is 0.001 to 0.2. The matrix rare earth metal element (designated by M in Formula 1) in these phosphors typically is lanthanum, gadolinium, yttrium, scandium, lutetium, or mixtures of these elements.
These phosphors are useful, e.g., in the field of x-ray intensifier screens. However, the spectral sensitivity of the x-ray film does not always precisely match the emission of the phosphor. Thus, it would be desirable to have the capability to adjust the green:blue emission ratio of the phosphor emission to tailor the phosphor emission to the spectral sensitivity of the x-ray film.
Accordingly, it is an object of the present invention to provide a terbium-activated rare earth oxysulfide phosphor which overcomes the disadvantages of the prior art.
It is another object of the invention to provide a terbium-activated rare earth oxysulfide phosphor in which the green:blue emission ratio of the phosphor emission is enhanced.
It is yet another object of the invention to provide a terbium-activated rare earth oxysulfide phosphor in which the phosphor emission can be tailored to match the spectral sensitivity of a particular x-ray film.
It is still another object of the invention to provide a method of enhancing the green:blue emission ratio of a terbium-activated rare earth oxysulfide phosphor.